The number of 911 calls made from wireless phones has been increasing steadily. For example, it is estimated that about 50 percent of the millions of emergency 911 (E911) calls in U.S. on daily basis are placed from wireless phones and the percentage is growing. A method for more accurately positioning a user equipment (UE) is needed to meet the US Federal Communications Commission (FCC) E911 requirements of newer generation of wireless. For example, one requirement for Long-Term Evolution (LTE) based wireless E911 calls is that the calling UE be located within 50 meters for 67% of calls and within 150 meters for 95%.
One common method for positioning a UE is based on an observed time difference of arrival (OTDOA). In this approach, a UE reports an observed time difference (OTD) relative to the serving base station such as LTE evolution node B (eNB) between a transmitting time of a reference signal and an observed arrival time at the UE of the reference signal. Two issues may affect accurately positioning a user equipment. One issue may be OTDOA hearability and another issue may be multipath issue. Due to the hearability issue, the signals from neighboring base stations are received with very low power. The multipath issue occurs when the reference signal takes different paths when propagating from a target neighbor cell to the UE, thus causing potential distortion of the observed arrival time of the reference signal.